Why, and how do I make them be displayed again? There are a few ways to make your documents appear in Preview. When you open the document, you can either: Preview for a few seconds to ensure you're working with the right document; or Choose Window > Preferences…> Preview You can also set a default or custom PDF viewer for Preview. Preview is the default viewer, though you can change it to another document format from the Preferences panel. You can also change your default PDF viewer manually. Open PDFs in Preview — OS X Tutorials If you click Preview: Choose Window/Preferences… at the top of the window, you can choose your PDF viewer for Preview. When you open a PDF in Preview, you can create a new document. Preview is used when you open a document that has the same layout of the original document. When the document is opened, it opens as a single PDF file, and the default PDF viewer is used. In this case, Preview is the correct PDF viewer. When you're looking for the page of the original document you want, click File > Page From Scanner. This opens the page in the default PDF viewer, and if you look at the Preview panel in the app, you'll see that Preview is the PDF viewer that has the same layout as the original document. If you need to remove a page, select the thumbnail of the blank page and click Remove. It doesn't show a single preview when I open a PDF. How do I change that? By default, Pages displays only one preview of a page before saving it into your document. If you want to see more than one, use the Page From File option — but note some PDF viewers will ask you for a page number before allowing you to save the document. If you want to save a PDF file using Page From File — OS X Tutorials I am getting the following error: Could not read the type declaration for 'File'> This is because I have the wrong version of the Adobe Reader plug-in installed : OS X 10.7.5 (Mountain Lion) Adobe Reader (184.108.40.206) > Adobe Reader 7.8.0 (220.127.116.11) > Adobe Acrobat Reader 7.7.5 (18.104.22.168) On macOS Sierra, an error message opens: Could not connect to the device.